Fig. 2. The absence of hypaxial Fgf10 expression correlates with a mammary phenotype in Pax3^ILZ/ILZ embryos. (A-D) X-Gal staining revealing Pax3-lacZ expression; the boxed area in A and B is magnified in C and D. The hypaxial buds, indicated by black arrowheads, of the somites (numbered) are absent in the mutant. (E-J) Whole-mount in situ hybridization at E11.25 (42 somite), E11.75 (48 somite) and E12.5 for Wnt10b, revealing the mammary line (between the arrows in E,F) and placodes (numbered in G-J), demonstrates late formation of placode 3 in the mutant. (K-P) Hematoxylin-Eosin stained sections through the plane indicated by the black line in E. The vertical line in K-N through the notochord illustrates the more dorsal position of the mammary line in mutants. The horizontal line with downwards arrows (M,N) demarcates the area containing cylindrical ectodermal cells, while the area between the asterisks (O,P) contains a stratum intermedium as a hallmark of the mammary line. Both areas are narrower in mutants. (Q-R) Whole-mount in situ hybridization for Fgf10 at E11.5. The hypaxial domain with high Fgf10 expression (black arrowheads) is absent in the mutant (R). Abbreviations: s, somite stage; sg, stratum germinativum; si, stratum intermedium; p, periderm. Scale bars: 10 µm in O,P; 100 µm in C-J,M,N,Q,R; 1 mm in A,B,K,L.